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# fileutil::magic::rt(n) 1.0 tcllib "file utilities"

## Name

fileutil::magic::rt - Runtime core for file type recognition engines written in pure Tcl

## Synopsis

- package require Tcl 8.4
- package require fileutil::magic::rt ?1.0?

- ::fileutil::magic::rt::open filename
- ::fileutil::magic::rt::close
- ::fileutil::magic::rt::file_start name
- ::fileutil::magic::rt::result ?msg?
- ::fileutil::magic::rt::resultv ?msg?
- ::fileutil::magic::rt::emit msg
- ::fileutil::magic::rt::offset where
- ::fileutil::magic::rt::Nv type offset ?qual?
- ::fileutil::magic::rt::N type offset comp val ?qual?
- ::fileutil::magic::rt::Nvx atlevel type offset ?qual?
- ::fileutil::magic::rt::Nx atlevel type offset comp val ?qual?
- ::fileutil::magic::rt::S offset comp val ?qual?
- ::fileutil::magic::rt::Sx atlevel offset comp val ?qual?
- ::fileutil::magic::rt::L newlevel
- ::fileutil::magic::rt::I base type delta
- ::fileutil::magic::rt::R offset

## Description

This package provides the runtime core for file type recognition engines written in pure Tcl and is thus used by all other packages in this module, i.e. the two frontend packages fileutil::magic::mimetypes and fileutil::magic::filetypes, and the two engine compiler packages fileutil::magic::cgen and fileutil::magic::cfront.

## COMMANDS

::fileutil::magic::rt::open filename

  This command initializes the runtime and prepares the file filename for use by the system. This command has to be invoked first, before any other command of this package.

  The command returns the channel handle of the opened file as its result.

::fileutil::magic::rt::close

  This command closes the last file opened via ::fileutil::magic::rt::open and shuts the runtime down. This command has to be invoked last, after the file has been dealt with completely. Afterward another invokation of ::fileutil::magic::rt::open is required to process another file.

  This command returns the empty string as its result.

::fileutil::magic::rt::file_start name

  This command marks the start of a magic file when debugging. It returns the empty string as its result.

::fileutil::magic::rt::result ?msg?

  This command returns the current result and stops processing.

  If msg is specified its text is added to the result before it is returned. See ::fileutil::magic::rt::emit for the allowed special character sequences.

::fileutil::magic::rt::resultv ?msg?

  This command returns the current result. In contrast to ::fileutil::magic::rt::result processing continues.

  If msg is specified its text is added to the result before it is returned. See ::fileutil::magic::rt::emit for the allowed special character sequences.

::fileutil::magic::rt::emit msg

  This command adds the text msg to the result buffer. The message may contain the following special character sequences. They will be replaced with buffered values before the message is added to the result. The command returns the empty string as its result.

  \b

    This sequence is removed

  %s

    Replaced with the last buffered string value.

  %ld

    Replaced with the last buffered numeric value.

  %d

    See above.

::fileutil::magic::rt::Nv type offset ?qual?

  This command fetches the numeric value with type from the absolute location offset and returns it as its result. The fetched value is further stored in the numeric buffer.

  If qual is specified it is considered to be a mask and applied to the fetched value before it is stored and returned. It has to have the form of a partial Tcl bit-wise expression, i.e.

      	& number

  For example:

      	Nv lelong 0 &0x8080ffff

  For the possible types see section NUMERIC TYPES.

::fileutil::magic::rt::N type offset comp val ?qual?

  This command behaves mostly like ::fileutil::magic::rt::Nv, except that it compares the fetched and masked value against val as specified with comp and returns the result of that comparison.

  The argument comp has to contain one of Tcl's comparison operators, and the comparison made will be

      	<val> <comp> <fetched-and-masked-value>

  The special comparison operator x signals that no comparison should be done, or, in other words, that the fetched value will always match val.

::fileutil::magic::rt::Nvx atlevel type offset ?qual?

  This command behaves like ::fileutil::magic::rt::Nv, except that it additionally remembers the location in the file after the fetch in the calling context, for the level atlevel, for later use by ::fileutil::magic::rt::R.

::fileutil::magic::rt::Nx atlevel type offset comp val ?qual?

  This command behaves like ::fileutil::magic::rt::N, except that it additionally remembers the location in the file after the fetch in the calling context, for the level atlevel, for later use by ::fileutil::magic::rt::R.

::fileutil::magic::rt::S offset comp val ?qual?

  This command behaves like ::fileutil::magic::rt::N, except that it fetches and compares strings, not numeric data. The fetched value is also stored in the internal string buffer instead of the numeric buffer.

::fileutil::magic::rt::Sx atlevel offset comp val ?qual?

  This command behaves like ::fileutil::magic::rt::S, except that it additionally remembers the location in the file after the fetch in the calling context, for the level atlevel, for later use by ::fileutil::magic::rt::R.

::fileutil::magic::rt::L newlevel

  This command sets the current level in the calling context to newlevel. The command returns the empty string as its result.

::fileutil::magic::rt::I base type delta

  This command handles base locations specified indirectly through the contents of the inspected file. It returns the sum of delta and the value of numeric type fetched from the absolute location base.

  For the possible types see section NUMERIC TYPES.

::fileutil::magic::rt::R offset

  This command handles base locations specified relative to the end of the last field one level above.

  In other words, the command computes an absolute location in the file based on the relative offset and returns it as its result. The base the offset is added to is the last location remembered for the level in the calling context.

## NUMERIC TYPES

byte

  8-bit integer

short

  16-bit integer, stored in native endianess

beshort

  see above, stored in big endian

leshort

  see above, stored in small/little endian

long

  32-bit integer, stored in native endianess

belong

  see above, stored in big endian

lelong

  see above, stored in small/little endian

All of the types above exit in an unsigned form as well. The type names are the same, with the character "u" added as prefix.

date

  32-bit integer timestamp, stored in native endianess

bedate

  see above, stored in big endian

ledate

  see above, stored in small/little endian

ldate

  32-bit integer timestamp, stored in native endianess

beldate

  see above, stored in big endian

leldate

  see above, stored in small/little endian

## Bugs, Ideas, Feedback

This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category fileutil :: magic of the Tcllib Trackers. Please also report any ideas for enhancements you may have for either package and/or documentation.

## See Also

file(1), fileutil, magic(5)

## Keywords

file recognition, file type, file utilities, mime, type

## Category

Programming tools